A power conversion device, such as a switching power supply device used for a motor drive system of an electric car or a hybrid car is required particularly to be downsized due to a vehicle space. To realize downsizing of the device, for example, it is considered to reduce the size of a passive element (such as a smoothing capacitor, an input reactor) used for the device. A size of the passive element can be reduced by increasing a drive frequency (switching frequency). However, such increase in the frequency causes increase in a switching loss, and power conversion efficiency may be deteriorated.
Under such circumstances, a technique is demanded for reducing a switching loss by adding a circuit which has a sufficiently compact size to restrict a size increasing of the device. For example, JP 2012-110208 A (corresponding to US 2012/0099348 A1) discloses a configuration in which a circuit including magnetic components is added to a switching power supply device having a bidirectional chopper. With such a configuration, a current flowing through a switching element and a voltage across both ends of the switching element are suppressed from overlapping with one another, and as a result, a switching loss is reduced.
However, in the configuration described in JP 2012-110208 A, four magnetic components, such as a transformer and an inductor are additionally necessary for reducing a switching loss of the bidirectional chopper. Usually, such a magnetic component has a larger size and needs higher cost compared with other circuit elements, such as a resistor or a capacitor. Consequently, the configuration described in JP 2012-110208 A also has a large size and requires a higher cost for manufacturing the device.